The present invention relates to a device used in used paper regeneration installations for the production of paper pulp.
As is known, the regeneration of used papers takes a more important place in the paper industry but it becomes more complex to carry out because of the proliferation of the contaminants such as sheets of plastic material, twines, pieces of glass etc.
This is why it has been proposed already, for example by EP-A-0 120 766, to use devices for separating a mixture of paper pulp and impurities removed at the bottom of the primary pulpers in which the used papers are shredded and mixed with water.
These widely used devices of known type are in the form of a generally closed revolving chamber having a substantially vertical wall provided with a perforated plate in front of which a blade member rotates.
Said chamber has an entrance situated opposite the perforated grid through which the mixture coming from the pulper is admitted, an outlet for the accepted pulp and another outlet for the contaminants.
The mixture filling the chamber is drawn by a pump situated behind the grid on screen, on the evacuation line of the paper pulp.
The blade member has as its only role to create a vacuum before the perforated grid with each passage of its blades so as to prevent the openings of the grid from becoming clogged by accumulations of impurities.
These devices although satisfactory, may present certain disadvantages in operation.
Thus, one may be confronted with the case of a contaminant of small cross section and of great length, for example a match, which becomes engaged in a perforation of the grid. In such a case, the vacuum created by the blade member before the grid does not suffice to extract the contaminant. On the contrary, the blades of the member may cut up the contaminant and thus create very small pieces which are then difficult to separate from the paper pulp.
Another problem that may occur has to do with the fact that the blade member being present solely for creating a vacuum for the cleaning of the grid, does not take along the liquid present in the chamber. The pulp is then set in motion only when it is near a blade and abruptly so; it is thus taken along by the blade when it comes up against the grid and is subjected to the suction of the pump. The different bodies present in the paper pulp are then subjected to a very strong acceleration which may produce fragmentation of contaminants.